The present invention relates to an internal combustion engine having a variable compression ratio mechanism, and more specifically relates to a technique for preventing an air-fuel ratio deviation that can be caused by a transient change in piston displacement volume under compression ratio control in the internal combustion engine. The present invention further relates to a control method for an internal combustion engine having a variable compression ratio mechanism.
Japanese Laid-Open Patent Publication No. 2001-263114 discloses one type of internal combustion engine having a variable compression ratio mechanism operatable during a piston intake stroke to control a compression ratio. This variable compression ratio mechanism includes a plurality of links (such as a connecting rod pivotally connected to a piston) and operates in such a manner that the compression ratio is set high in a low/middle-load engine operating range, or is set low in a low/middle-speed high-load engine operating range and high in a low/middle-speed low/middle-load engine operating range. By controlling the compression ratio in accordance with the engine speed and load as above, the engine can achieve a good balance of fuel economy and power output.